The automotive industry employs steel having coatings which are substantially corrosion resistant and which withstand the stress and stretching of sheet metal stamping and forming operations. Coatings currently in use include a base coat of a proprietary composition containing zinc and chromic acid and a top coating of a linear high molecular weight epoxy resin or phenoxy resin containing zinc. Such is well described in an article by Dr. Alexander W. Kennedy entitled "ZINCROMETAL:COIL COATINGS ANSWER TO CORROSION" published in MODERN PAINT AND COATINGS, Sept. 1976, pages 21-26.
These high molecular weight epoxy or phenoxy resins employed as the binder in such coatings have weight average molecular weights of about 30,000 and above. The coatings of the present invention are equal to or superior to these binders in the double draw test while having weight average molecular weights much less e.g. less than about 10,000.
The present invention is directed to an improvement in a weldable coating composition comprising an electrically conductive pigment, an epoxy resin binder and solvent wherein the improvement resides in employing as the resin binder, the reaction product of